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MANGANESE DIOXIDE                                75

content of Mn02, determination of which is the principal aim of the analysis ;
the latter may, however, be extended to the determination of moisture,
total manganese, carbon dioxide and any other extraneous matters.

1.  Moisture.—1-2 grams of the finely powdered substance are dried
at 100° for 6 hours.

2.  Determination of the Manganese Dioxide (Lunge's method).—
1-0866 gram of the dry substance is mixed, in a 300 c.c. flask furnished with
a Bunsen valve (see Limestones and Clays), with 75 c.c. of ferrous sulphate
solution (100 grams of the pure sulphate or the corresponding quantity of
ferrous ammonium sulphate, and 100 c.c. of cone, pure sulphuric acid in
i litre), the titre of which has been recently determined with N/2-perman-
ganate (15-815 grams of pure permanganate per litre).    The flask is closed
and heated until all the pyrolusite is acted on, that is, until no brown deposit
remains.    When cool, the liquid is diluted with about 200 c.c. of boiled
water and titrated with the permanganate solution until the pink coloration
persists for half a minute.    The difference between the number of c.c. of
permanganate used to titrate the 75 c.c. of the ferrous solution and that
used in the test gives, when multiplied by 2, the percentage of Mn02 in
the substance (i c.c. of the KMn04 = 0-02173 gram of Mn02).

3.  Determination of the Total Manganese.—1-0875 gram is treated
with cone, hydrochloric acid until evolution of chlorine ceases, the excess of
acid being neutralised with pure, precipitated calcium carbonate and con-
centrated, filtered chloride of lime solution added ;   after heating for a
few minutes the liquid is decolorised by addition of alcohol, drop by drop.
The whole of the manganese is then precipitated as dioxide (the filtrate
should not turn brown on further addition of chloride of lime).   The pre-
cipitate is filtered off and washed until the wash-water no longer colours
starch-iodide paper, and is then treated with ferrous sulphate as in 2.   The
manganese is calculated as Mn02.

4.  Carbon Dioxide.—This is determined as in chalk (see Chapter on
Cement Materials).

5.  Other Tests.—For the detection and determination of the various
foreign substances  (see above) the ordinary analytical methods may be
followed.   Tests are made more particularly for oxides of iron and other
metals, lime, baryta, silica and phosphoric acid.

In general, pyrolusite contains 35-85% MnO2 (the purer, well crystallised
product may contain about 90%). The qualities to be used for making chlorine
should contain, if of German origin, not less than 60% MnO2, or, if of Spanish
origin, not less than 70%. Extraneous matters may be present in the follow-
ing proportions : ferric oxide, up to 30% ; alumina, up to 4% ; lime, up to 4% ;
silica, up to 20% ; and phosphoric acid, up to i%. The manganese minerals
for the manufacture of glass should be free from coloured oxides (iron, nickel,
cobalt, copper) ; those for the treatment of iron or steel should not contain
heavy spar, sulphides, copper, nickel, cobalt or phosphorus, and should be poor
in silica.